I thought I would write a fun article today since the start of a weekend is a time that many people who have disciplined eating habits consider their “cheat” days. In the past, I have frequently discussed the difference between articles that are found in peer-review journals versus those published in so-called “throw away” journals. I have talked about the type and the way a specific study was conducted and how the researchers collect the information/evidence. The gold standard of any trial is to have what is called Level 1 evidence. This means that the study was randomized, blinded to the researchers, controlled, with a statistically significant primary endpoint being reached. For example, this could be a study comparing two drugs or a drug versus a placebo given to different people. The researchers do not know who is given what medication. The study is rigorously controlled and the goal of the study (primary endpoint) with one drug being superior to the other is clearly reached with statistical significance. However, some studies cannot be performed in this fashion for a multitude of reasons. The main thing to remember is that in most studies association does not mean causation. It is with this background that we will talk about chocolate and stroke prevention.
In the October 18, 2011 issue of the Journal of the American College of Cardiology, Dr. Susanna Larsson of the National Institute of Environmental Medicine in Stockholm, Sweden stated in a news release that women who ate up to 2 bars of chocolate per week showed a significantly reduced risk of stroke. Those women who ate up to a half of a bar or even smaller amounts also had a reduction in the stroke rate. The study included 33,372 women who answered a food-frequency questionnaire. They were asked to report how often and how much chocolate they consumed, including a variety of other foods for a year time span. Investigators listed the women into categories ranging from those who never ate chocolate to those who indulged three or more times a week and examined the risk of stroke over a mean follow-up of 10 years, adjusting for major risk factors associated with stroke. Women who reported having been diagnosed with hypertension did not show any significant benefit; however, those without hypertension and higher chocolate consumption seemed to show a marked decrease in stroke reduction. The researchers identified 1549 strokes in their study.
I know this sounds great to chocolate lovers, but the biggest problem was not related to chocolate. It was the way the study was conducted. The women were given a food frequency questionnaire and from this such wonderful results were reported. I don’t remember what I ate yesterday let alone keeping track of everything for a year. Then a great statistician was brought in to adjust the data and was some how able to exclude everything else that may impact stroke rates. And now you have a study saying that Swedish women who ate a certain amount of chocolate had lower stroke rates than those who did not. This information actually made the television news. The association with chocolate consumption and stroke was stronger with higher concentration of cocoa in the chocolate.
A large analysis also from Sweden in 2012 followed 37,103 Swedish men for ten years. The Swedish results similarly showed that those who reported the highest chocolate consumption, averaging 62.9 grams (a little more than 2 ounces) per week, had the lowest stroke risk.
In 2015, the journal HEART published results from the EPIC Norfolk study. The EPIC (European Prospective Investigation into Cancer) Norfolk study is a population-based prospective cohort study. The study recruited over 30,000 men and women aged 40-79 years at baseline between 1993 and 1998 from 35 participating general practices in Norfolk. Individuals provided information about behavioural factors, including diet and physical activity, and attended a baseline health check including the provision of blood samples for concurrent and future analysis and the collection of anthropometric data. The participants have continued to provide follow up data and attend additional health checks for over 25 years. A careful analysis of food diaries completed by participants determined that those who reported the highest levels of chocolate consumption experienced lower rates of stroke throughout an almost 20 year follow up period, while those who reported very low or no chocolate consumption had the highest rates of stroke.
An even larger meta-analysis examined a larger group, a total of 157,809 participants from nine different studies, and found the same trend.
It's important to note that all these studies are observational, meaning they just look for correlations between risk factors and outcomes. They can't prove conclusively that chocolate is what reduced participant’s stroke risk. It's possible that people who eat more chocolate also have other healthy characteristics that help to prevent stroke.
So what are the health properties of chocolate? Researchers have long thought that cocoa, the main ingredient in chocolate, may have cardiovascular benefits due to the flavonoids in cocoa and their antioxidant properties. Antioxidants protect the body from damage caused by free radicals and can suppress oxidation of low-density lipoprotein particles which are the carriers of the bad cholesterol in the blood and drive the cholesterol into the artery wall causing atherosclerosis. Dark-chocolate consumption has also been shown to reduce blood pressure, which is a major risk factor for stroke, but the data is limited at best.
Now the question from chocoholics, who just love their chocolate, is how much should one eat? Chocolate, and especially chocolate bars, are high in sugar, fat, and calories. Dark chocolate, with a concentration of greater than 50% cocoa, is usually lower in sugar and has higher flavonoid content. Indulgence in chocolate in moderation remains a reasonable approach to satisfy a craving. Eating a healthy diet, controlling blood pressure, cholesterol levels, and modifying other risk factors for stroke is the best approach for now.